The present embodiments relate to a liquid metal bearing.
A liquid metal bearing is known, for example, from DE 195 23 162 A1.
The known liquid metal bearing includes at least one first bearing part and at least one second bearing part. The at least one first bearing part and the at least one second bearing part have a non-positive fit connection to one another.
With the liquid metal bearing known from DE 195 23 162 A1, an aluminum oxide (Al2O3) coating or a titanium oxide (TiO2) coating is applied to the surfaces of the bearing parts made of molybdenum by a physical vapor deposition (PVD) process. The coating thicknesses able to be realized by the process lies between approximately 0.1 μm and approximately 1 μm. Even with the maximum possible coating thickness, the rough surface of the bearing parts resulting from machining (e.g., average roughness Ra of approximately 2 μm) may not be completely covered. The rough molybdenum surface may not be planarized by PVD methods.
The aluminum oxide or titanium oxide coatings applied to the surfaces of the bearing parts are relatively hard, so that no “meshing” of surfaces pressed onto one another may be provided. This leads, with increasing stresses being imposed on the liquid metal bearings (e.g., higher rotational speeds, higher temperatures), to increasingly smaller production tolerances (e.g., less than 2 μm) having to be adhered to, so that the applied PVD coatings withstand the increasing pressure of the liquid metal (e.g., prevent the liquid metal escaping).
As a result of the higher evaporation rate during coating (e.g., short process time) and the “granularity” of the evaporation material (e.g., granulate or beads of Al2O3 with a diameter of approximately 1 mm) during vapor deposition using an electron beam, small “beads” are released from the vapor deposition material, which then remain adhering to the surface of the bearing parts. Even when the two bearing parts are pressed together, no change is visible to such beads. This is because of the actual gap present between the bearing parts (e.g., greater than the diameter of most of the beads) and because of the hardness of the aluminum oxide, so that disadvantageously a larger bearing gap arises than is predetermined by the planarity of the bearing parts.